BEIJING — Thousands of people in an eastern Chinese city clashed with police at a protest on the proposed expansion of a petrochemical factory that they fear will spew pollution and damage public health, residents said Saturday.
It was the latest in a string of protests in China this year because of fears of health risks from industrial projects, as members of the rising middle class become more outspoken against environmentally risky projects.
Past protests have targeted a coal-fired power plant in southern China, a wastewater pipeline in eastern China, and a copper plant in west-central China.
The Zhenhai district government in Zhejiang Province’s Ningbo city said in a statement Saturday that ‘‘a few’’ people disrupted public order by staging sit-ins, unfurling banners, distributing fliers, and obstructing roads. It said the proposed project is under evaluation and the public has opportunities to offer input.
Zhenhai police said protesters threw rocks and bricks at officers Friday and that police dispersed illegal gatherings to restore the flow of traffic.
Residents, however, said the protests involved thousands of people and turned violent after authorities used tear gas to dispel the crowds and arrested participants.
‘‘It started with a peaceful petition but turned into a citywide riot,’’ said a local resident who gave only his family name, Ren, because he had come under police watch. He said he was called in by police because of his frequent online postings about the project, which would produce chemicals such as ethylene and paraxylene.
Ren said the protests intensified Friday when young residents returned home for the weekend. He said 4,000 to 5,000 people blocked major road entrances to the district and that the public grew angry when police arrested three college students and used tear gas on the crowds.
He said demonstrators overturned a car, and some smashed the door of a fire truck that arrived to hose off leaked gasoline as well as to disperse protesters.
Thousands of protesters stormed a local police station, where they demanded the students’ release and a dialogue with district officials. Ren said the protesters also went to a traffic police compound, where they overturned police vehicles and private cars.
He said riot police moved in to form a shield to guard the traffic police compound and that protesters threw rocks and water bottles at the riot police.
Later Friday night, police began beating protesters and passersby with batons, Ren said.
On Saturday, protesters gathered in a large public square in Ningbo and shouted slogans against the project, Ren said. Many were taken away by police, he said.
Among the protesters was a businessman who said he was taken to a police station where he was forced to delete photos of the protest he had taken with his cellphone. He said he was released after an hour.
‘‘The police have my information, and I need to keep a low profile,’’ said the man, who gave only his family name, Wang.